Auto-adhering one-component RTV silicone sealant composition utilizing an adhesion promoter

ABSTRACT

An auto-adhering one-component room temperature vulcanizable silicone sealant composition generally utilizing a di-substituted mixed oxime-alkoxysilyalkyl area adhesion promoter compound. The sealant has low odor, is non-corrosive to ferrous or aluminum substrates, has good adhesion to many types of substrates, and eliminates the need for a silicone resin primer. In addition, it exhibits surprisingly good adhesion to oil contaminated surfaces.

TECHNICAL FIELD

The present invention relates to an auto-adhering one-component RTVsilicone sealant. More specifically, the present invention relates tothe utilization of a di-substituted mixed oxime-alkoxysilylakyl ureacompound as an adhesion promoter in the sealant.

BACKGROUND

Heretofore, low modulus characteristics of silicone rubbers have beendesirable in accommodating joint movement due to vibration and thermalcycling since less stress is exerted on sealant-metal bond interface.Such low modulus properties generally decrease the probability of oilleaks. However, oil resistance has been traditionally improved byutilizing comparatively high crosslink densitites. The result was lowerelongation properties and, hence, reduced movement capabilities. Whenfewer crosslinks were incorporated into the elastomer to lower themodulus, generally more rapid deterioration of the polymer backbone bynucleophilic or electrophilic agents occurred at elevated temperatures.Accordingly, room temperature vulcanizable elastomers having good oilresistance were generally not made.

U.S. Pat. No. 3,189,576 to Sweet relates to oxime curatives and to neworganosilicon intermediates.

U.S. Pat. No. 4,323,489 as well as U.S. Pat. No. 3,962,160, both toBeers, generally relate to oxime curable room temperature vulcanizates.More specifically, the '489 patent relates to a vulcanizable siliconerubber composition with very low modulus containing a silanolend-stopped diorganopolysiloxane, a difunctional acetamide coupler as achain extender and a minor amount of a compound containing an oximefunctionality thereon as a trifunctional crosslinker.

U.S. Pat. No. 4,356,116 to Beers relates to a low volatile roomtemperature vulcanizable silicone rubber composition containing variouscomponents including a silanol polymer, a crosslinking agent, and afiller.

U.S. Pat. No. 3,517,001 to Berger relates to adhesion promotercompositions.

U.S. Pat. No. 4,100,129 to Beers also relates to adhesion promotercompositions curable in the presence of moisture.

U.S. Pat. No. 4,395,526 to White et al relates to a stable,substantially acid-free, one-component curable polyalkoxy-terminatedorganpolysiloxane composition having a condensation catalyst, such as atin compound. The material in this patent also serves as an adhesionpromoter.

Specific patents relating to acetoxy curing room temperaturevulcanizable silicones include Ceyzeriat, U.S. Pat. No. 3,133,891,Brunner, U.S. Pat. No. 3,035,016, and Beers, U.S. Pat. No. 3,382,205.More specifically, the Beers' patent relates to organopolysiloxanecompositions comprising a mixture of organotriacyloxysilane and a basemixture containing organosiloxane having chemically combined organsiloxyunits.

U.S. Pat. No. 3,541,044 to Beers relates to a substantially anhydrousorganopolysiloxane composition curable to the elastomeric state uponexposure to moisture. Another patent by Beers, namely U.S. Pat. No.3,837,878 relates to a two-component room temperature vulcanizablesilicone rubber composition suitable for molding applications whereasU.S. Pat. No. 3,837,878 also to Beers relates to a process for treatingsilicone fillers.

U.S. Pat. No. 3,776,933 to Toporcerer relates to chain extenders withregard to RTV systems.

While most of the above patents do relate to organopolysiloxanecompositions, they do not teach one-component room temperaturevulcanizable silicone sealant composition of the present invention or adi-substituted mixed oxime-alkoxysilylalkyl urea derivative as anadhesion promoter.

DISCLOSURE OF INVENTION

It is therefore an aspect of the present invention to provide anadhesion promoter.

It is yet a further aspect of the present invention to provide anadhesion promoter as above, wherein said adhesion promoter can be madevia the reaction product of an alkoxysilylalkylamine.

It is another aspect of the present invention to provide anauto-adhering one-component room temperature vulcanizable siliconesealant containing an adhesion promoter which sealant is non-corrosivewith regard to iron containing and aluminum substrates.

It is still another aspect of the present invention to provide anauto-adhering one-component room temperature vulcanizable siliconesealant containing an adhesion promoter as above, wherein no primer isrequired to be initially applied to said substrate.

It is yet another aspect of the present invention to provide a sealantwhich will bond to oil contaminated surfaces.

The compositions of the present invention generally exhibit outstandingauto-adhering adhesion even an oil contaminated metals such as thealuminum and steel surfaces encountered in the auto industry. Thesecompositions also have excellent oil-resistant properties including oilresistance at elevated temperatures, for example 300° F., and areparticularly useful as silicone formed-in-place gasketing.

An auto-adhering one-component room temperature vulcanizable siliconesealant compound of the present invention has an adhesion promoter ofthe following formula: ##STR1##

R¹ and R⁶ are independently a non-aromatic hydrocarbyl or halosubstituted hydrocarbyl group or a carboxyalkyl group having 1 to 10carbon atoms. R², R³, R⁷ and R⁸ are independently H, hydrocarbyl orhalohydrocarbyl, either of which may be aromatic or non-aromatic, orcarboxyalkyl having 1 to 10 carbon atoms. R⁴ and R⁵ are divalenthydrocarbon or halohydrocarbon groups of 1 to 20 carbon atoms, suitably1 to 10 carbon atoms.

The non-aromatic hydrocarbyl groups may be aliphatic or cycloaliphatic,saturated or unsaturated groups including alkyl, alkenyl, alkynyl,cycloalkyl etc. Aromatic hydrocarbyl groups include aliphaticsubstituted aromatic and aromatic substituted aliphatic groups.

R¹ and R⁶ are preferably methyl or ethyl. R² and R³ are preferably alkylsuch as methyl or ethyl.

R⁴ and R⁵ are preferably C₃ -C₈ alkylene groups. R⁷ and R⁸ are desirablyalkyl such as methyl or ethyl. Preferably R⁷ and R⁸ are hydrogen.

The numerals designated by a, b, f, and e, are independently 0-3; g andh are 0 or 1; and a+b+g=f+e+h=3. Suitably b and f are 1 to 3. Preferablya and e are 1, b and f are 2 and g and h are 0.

Examples of specific adhesion promoters include the following: ##STR2##

The actual adhesion promoter often is a statistical mixture of the aboveformulations and/or of the "general formula" set forth above. Wheneverformula 1 or 2 is utilized, it is desirable that a compound of formulas3 through 5 also be utilized so that a more reactive oxime group exists.

When the various end segments, that is (R'O)_(a) and (OR⁶)_(e) aredifferent, for example, (R'O)_(a) is trimethoxy and (OR⁶)_(e) istriethoxy, the adhesion promoter is a liquid. In other words,unsymmetrical end groups yield a liquid. Thus, it was thought that whenthe end groups are symmetrical, the adhesion promoter would also be aliquid. However, when symmetrical end segements or groups such astriethoxy were utilized, the promoter unexpectedly was a solid. This istruly an unexpected result since the end group segments constitute avery small portion of the structure. Inasmuch as liquids are easier tohandle, unsymmetrical end segments or groups are preferred.

The adhesion promoter of the present invention can be made in a numberof different ways. A desired mode of preparation involves reacting acompound of Formula A with Formula B. ##STR3##

R¹, R⁴, R⁵, R⁶ as well as a and e are set forth above. The reaction isexothermic and spontaneous upon mixing the two (2) ingredients together.The reaction is generally carried out in the presence of an inert gasblanket such as nitrogen to avoid reaction of the compound withmoisture.

Generally, from about 0.95 to about 1.0 moles of Formula B is utilizedper mole of Formula A with an equal molar ratio being preferred althoughmuch larger or smaller amounts can be utilized. The reaction is carriedout at atmospheric pressure at a temperature of from about 40° C. toabout 100° C. Formula (B) is slowly added to (A) while stirring in a 3neck flask equipped with a thermometer and blanketed with nitrogen.

Reaction of a compound of Formulas A and B results in a compound ofFormula C. ##STR4##

The oxime crosslinking units can be grafted to the compound of Formula Cby heating with an oxime compound at a temperature of from about 45° C.to about 150° C., preferably from about 50° C. to about 120° C. beingpreferred. Once again, an inert gas blanket, for example nitrogen, isutilized to avoid reaction with moisture. The type of oxime compoundsutilized are generally oxime crosslinkers set forth in Formulas Type Iand Type II or mixtures thereof. ##STR5##

R¹⁰ is generally an alkyl having from 1 to 8 carbon atoms with methylbeing preferred, an alkenyl having from 2 to 8 carbon atoms with vinylbeing preferred, a haloalkyl having from one to eight carbon atoms, atrifluoralkyl having from one to eight carbon atoms, or a haloalkyenylhaving from two to eight carbon atoms.

R⁹ is a hydrocarbyl, a halohydrocarbyl, or a carboxyalkyl having from 1to 10 carbon atoms, preferably R⁹ is methyl or ethyl.

Preparation of the oxime compounds set forth in the Type I and Type IIformulae is generally well known to the art as set forth in U.S. Pat.No. 3,189,576, which is hereby fully incorporated by reference as to thepreparation thereof.

Generally, the greater the number of oxime groups on the silicon atom ofthe adhesion promoter the better the adhesion. Adhesion is also effectedby the R group on the crosslinker. It is particularly enhanced when sucha group is alkenyl. Oftentime, the oxime type crosslinker utilized tomake the silicone sealant of the present invention can be a mixture.That is, from about 5 percent to about 40 percent and preferably fromabout 10 percent to about 20 percent by weight of an oxime compoundhaving the formulation of the Type I oxime can be utilized based uponthe total weight of oxime compounds in the entire formulation.Similarly, from about 60 to about 95 percent, and preferably from about80 to about 90 percent of a Type II oxime can be utilized based upon thetotal weight of all oxime compounds in the composition. Considered on amolar basis, from about 0.05 moles to about 0.4 moles of the Type Ioxime, and preferably from about 0.1 to about 0.2 moles is utilized per1 mole of Type I and II oxime compound.

Considering the sealant composition of the present invention, itcontains a silanol terminated diorganosiloxane polymer as the basicingredient. This linear polymer may be devolatilized in a manner such asset forth in U.S. Pat. No. 4,356,116 and generally has a viscosity offrom about 2,000 to about 250,000 centipoise at 25° C. and preferablyfrom about 10,000 to about 120,000 centipoise. The polymer has theformula ##STR6## where n is from about 300 to about 1,000, where R¹¹ andR¹² can be the same or different, where R¹¹ and R¹² is an alkyl grouphaving from 1 to 8 carbon atoms with methyl being preferred, acycloalkyl group having from 4 to 7 carbon atoms such as cyclohexyl, analkenyl group having from 2 to 8 carbon atoms with vinyl beingpreferred, an aryl or an alkyl substituted aryl group having from 6 to14 carbon atoms such as phenyl, methylphenyl, or a fluoralkyl grouphaving from one to eight carbon atoms with 3,3,3-trifluoropropyl beingpreferred. The amount of the linear polymer generally ranges from about25 to about 90 percent by weight and preferably from 30 to about 60percent by weight based upon the total weight of the low modulus RTVsilicone composition. Such polymers are commercially available and aremanufactured by Mobay, Union Carbide and Wacker Chemie.

The sealant composition further comprises the adhesion promoter of theinvention, which may be mixed with oxime crosslinking agents, andoptionally a plasticizer.

In order to insure that gellation or viscosity increases do not occur,an excess of the adhesion promoter containing the oxime crosslinkingagents to the silanol in the base polymer is utilized at a ratio of fromabout 1.2 to about 4.0 with from about 2.0 to about 3.0 being preferred,molar ratio of crosslinker to silanol groups.

Considering the adhesion promoter, the amount thereof is from about 0.5to about 3 percent by weight with from about 0.8 to about 2 percent byweight being preferred based upon the total weight of the sealantcomposition.

An organo tin catalyst is desirably utilized in the composition topromote reaction of the oxime compounds and silicone polymer. The amountof said catalyst is generally from about 0.01 to about 0.5 percent byweight and preferably from about 0.02 to about 0.2 percent by weightbased upon the total weight of the sealant composition.

Examples of organo tin catalysts are well known to the art and includethose set forth in U.S. Pat. Nos. 4,356,116 and 4,395,526, hereby fullyincorporated by reference. Examples of specific tin compounds includedisbutyltindilaurate, dibutyltindiacetate, tin octoate,dimethyltindibutyrate, triethyltintartrate, tin oleate, dibutyltinoxide,and dimethyltinbisneodecanoate, and the like.

The plasticizer utilized along with the linear base polymer in thesealant composition is a devolatilized triorganosiloxy terminated withdiorganopolysiloxane fluid existing in an amount of from 0 to 1 to about40 percent by weight and desirably from 5 to about 25 twenty-fivepercent by weight based upon the total siloxane composition. Theplasticizer lowers the durometer and modulus of the cured rubber and,lowers the viscosity of the overall system or composition. However, theviscosity of the plasticizer should not be too low in as much as it willtend to bleed out of the composition. Accordingly, the viscositygenerally ranges from about 50 to 100,000 centipoise and preferably fromabout 500 to about 10,000 centipoise.

The plasticizer is a diorganopolysiloxane polymer terminated withmonofunctional, triorgano siloxy end groups. The organo compounds withinthe repeating units are the same as R¹¹ and R¹² set forth herein abovewith regard to the base polymer. However, it may contain tracequantities of trifunctional monoorganosiloxy units originating fromimpurities in the starting materials. The siloxy units contain an alkylgroup having from 1 to 8 carbon atoms with methyl being preferred. Thenumber of repeating units in the plasticizer is generally from about 20to about 900. As with the linear base polymer, the plasticizer isdevolatilized in accordance with any conventional manner or process,well known to the art. A specific example of devolatilization is setforth in U.S. Pat. No. 4,356,116 which is hereby fully incorporated byreference.

In order to reinforce the polymer network as well as to impart non-sagproperties to the system, a thixotropic agent is added to the overallcomposition. This agent which also adds physical strength to the systemdesirably is a treated fumed silica filler being preferred. Treatedsilica fillers generally have lower moisture content, and result inbetter low modulus properties. The amount of silica filler generallyranges from about 1 to about 20 percent by weight and from about 3 toabout 8 percent by weight being preferred. Treated or untreated silicafillers are well known to the art and generally any such conventionalfiller can be utilized. Examples of specific silica fillers are setforth in U.S. Pat. No. 3,837,878 which is hereby fully incorporated byreference. Additionally, treated silica as set forth in Lucas U.S. Pat.No. 2,938,009, Lichtenwalner U.S. Pat. No. 3,004,859, and Smith U.S.Pat. No. 3,635,743, all hereby fully incorporated by reference, can beutilized. Typically, the silica filler has a very high surface area suchas about 200 M² /gram.

Optionally, from about 0.1 to about 5 percent by weight and preferablyfrom about 0.2 to about 3 percent by weight based upon the total weightof the overall system or composition of a thermal aging additive can beutilized. This optional component functions to reduce oxidation andthermal rearrangement of polymers at elevated temperatures. Theseantioxidants may include materials like cerium neodencanoate, rare earthoctoates and iron octoate. Representative samples can also includethermal aging additives such as carbon black, iron oxide powder, andtitanium dioxide. Naturally, other pigments can be utilized to impartvarious desired colors.

Another optional ingredient is an inert semi or non-reinforcing fillersuch as ground quartz, calcium carbonate, talc, clay, various silicatecompounds and other materials or their treated counterparts well knownin the art. The amount utilized is from about 5 percent to about 60percent by weight based upon the total weight of the sealantcomposition.

The silicone sealants of the present invention are useful in that theycure at room temperature. Moreover, the need for applying a primerprecoat to a substrate to obtain good adhesion is also eliminated. Thesilicone sealants moreover have a low odor and give good adhesion tovarious substrates such as glass, ceramics, various metals such asaluminum, steel and the like, as well as various plastics, such asacrylates, fiberglass reinforced polyesters andacrylonitrile-butadiene-styrene terpolymers. The sealants also exhibitexcellent oil resistance at elevated temperatures of about 300° F. Thus,such sealants find use wherever such properties are desired. Specificexamples of utility include RTV silicone adhesives, as for examples,gaskets, bath tub caulking compounds, masonry joint materials, plasticadhesives, and the like. A desired use is an automobile engine sealantsas for example, valve cover gaskets, oil pan gaskets, and the like.

The preparation and incorporation of the aforementioned silane adhesionpromoter into a silicone sealant composition can be accomplishedaccording to one of two modes: The first mode involves a reactionproduct of various oxime type compounds and thus the exact end productis a mixture while in the second mode, a specific oxime product isproduced.

In the first mode of preparation about 0.5 to 4 parts of an equimolarmixture of a compound of prereacted Formula A and a compound of FormulaB is prepared by mixing under dry nitrogen for about one hour to up to60° C. is added to the crosslinker mixture consisting of about 12 partsof the oxime curing agent set forth above and 0.2 parts of an organotinsalt catalyst as also set forth above and this mixture is heated at 50°C. for 10 to 20 hours in a closed container.

The silicone sealant compounds is then prepared by charging the variousingredients into a mixture under dry conditions as through the use ofdry nitrogen to prevent hydrolysis of the oxime crosslinking compound.Generally, the polymer is added first with the plasticizer. The oximecomposition is mixed under high speed or agitation as well as under avacuum for several minutes or even hours to remove the entrappednitrogen bubbles. The resulting paste formed can be placed or extrudedinto a desirable container and the like.

The invention will be better understood by reference to the followingexample:

EXAMPLE 1

    ______________________________________                                                                 Weight                                                                        %                                                    ______________________________________                                        1.     10,000 cps, viscosity silanol termin-                                                                 40.06                                                 ated polydimethylsiloxane                                              2.     1000 cps trimethylsilyl terminated                                                                    15.46                                                 polydimethylsiloxane                                                   3.     Stearic acid treated calcium                                                                          34.05                                                 carbonate                                                              4.     Polydimethylsiloxane treated fumed                                                                    3.61                                                  silica having a surface area of                                               approximately 200 m.sup.2 /gram                                        5.     Iron oxide              1.40                                           6.     Methyltris-methylethylketoximos-                                                                      4.81                                                  ilane                                                                  7.     Dimethyltinbisneodecanoate                                                                            0.08                                           8.     Equimolar mixture of gamma isocyanato                                                                 0.53                                                  propyl trimethoxy silane and gamma                                            aminopropyl triethoxysilane                                            ______________________________________                                    

This composition was prepared by charging the ingredients into themixing can of a vertical laboratory change can mixer which had beenflushed with dry nitrogen to prevent the hydrolysis of the oximecrosslinker and adhesion promoter.

Ingredients (6), (7) and (8) were heated in a closed glass jar in a 50°C. oven for 16 hours and allowed to cool before incorporation into thesealant formulation. The ingredients were subsequently added as follows:(1), (2), (3), (4), (5), then the mixture of (6), (7) and (8). Thenmixed at high speed under vacuum for approximately two hours andafterwards the resulting paste was transferred to a pressure Semcomixer. It was then extruded from the pressure Semco into six ouncepolyethylene cartridges.

It was found that the 180° C. peel adhesion of this sealant to alcladaluminum after curing for 14 days was 12 to 13 pounds per linear inchwith 100% cohesive failure versus 0 to 2 pounds per linear inch with100% adhesive failure for a sealant without (8).

In the second mode of preparation an equimolar mixture of a compound offormula A and a compound of formula B are allowed to react at roomtemperature and atmospheric pressure preferably under an inert gasblanket and a sufficient amount of a ketoxime compound such asmethylethylketoxime is added to the reaction product and the mixtureheated to cause partial substitution of ketoxime on the silicon atom bydisplacement of the alkoxy moieties. The sealant is then prepared as inthe first mode of preparation.

This mode of preparation can be better understood by reference to thefollowing examples:

EXAMPLE 2

44.2 g (0.2 moles) of gamma aminopropyl triethoxysilane was addeddropwise to 41.0 g (0.2 mole) of gamme isocyanatopropyl trimethoxysilaneat room temperature and atmospheric pressure under a nitrogen blanket.The addition was done slowly to avoid excessive heat build-up from thereaction exotherm. When the addition was complete 38.3 g (0.44 mole) ofmethyl ethylketoxime was added to the reaction product and the mixturewas heated to 120° C. for about 4 hours. The resulting analysis by gaschromatograph indicated a mixture of the substitution products ofmethylethyl ketoximo moieties on the silicon atom.

EXAMPLE 3

    ______________________________________                                                               Weight                                                                        %                                                      ______________________________________                                        1.     10,000 cps. viscosity silanol                                                                       40.06                                                   terminated polydimethylsiloxane                                        2.     1000 cps trimethylsilyl terminated                                                                  15.46                                                   polydimethylsiloxane                                                   3.     Stearic acid treated calcium                                                                        34.05                                                   carbonate                                                              4.     Polydimethylsiloxane treated fumed                                                                  3.61                                                    silica having a surface area of                                               approximately 200 m.sup.2 /gram                                        5.     Iron oxide            1.40                                             6.     Methyltris-methylethylketoximosilane                                                                4.81                                             7.     Dimethyltinbisneodecanoate                                                                          0.08                                             8.     The material of example 2                                                                           0.53                                             ______________________________________                                    

This composition was prepared as in Example 1. The ingredients wereadded in the order: (1), (2), (3), (4), (5), (6), (7), and (8), thenmixed at high speed under vacuum for approximately two hours andafterward the resulting paste was transferred to a pressure Semco mixerand extruded into six ounce polyethylene cartridges. The peel adhesionof this sealant to Alclad aluminum after curing for four weeks was 23pli with 100% cohesive failure.

Accordingly, it can be seen that a significant increase in adhesionoccurs utilizing the adhesion promoter of the present invention.

Examples Demonstrating the Utility of Mixed Oxime Alkoxy Silyalkyl UreaAdhesion Promoters EXAMPLE 4

    ______________________________________                                        (1)     80,000 cps. viscosity silanol                                                                      39.81                                                    terminated polydimethylsiloxane                                       (2)     1000 cps. trimethylsilyl terminated                                                                15.36                                                    polydimethylsiloxane                                                  (3)     Stearic acid treated calcium                                                                       33.83                                                    carborate                                                             (4)     Raven 1020 carbon black                                                                            1.07                                             (5)     Polydimethylsiloxane treated fumed                                                                 3.58                                                     silica having a surface area of                                               approximately 200 M.sup.2 /gram                                       (6)     Vinyl tris-methylethylketoximo-                                                                    4.78                                                     silane                                                                (7)     Dimethyltinbis-neodecanoate                                                                        0.08                                             (8)     N--(3-trimethoxysilylpropyl)-                                                                      1.49                                                     N'--(3-triethoxysiylpropyl)urea                                       ______________________________________                                    

The above composition was prepared by charging the following ingredientsto the mixer under dry nitrogen to prevent hydrolysis. (1) was added tothe mixer followed by (6), (3), (4), (5), (2), (8) and (7).

The resulting paste was then made into ASTM sheets. The test sheets werethen allowed to cure for seven days. The initial cured and two week oilimmersion properties were then determined. The oil immersion tests wereperformed after two weeks (14 days) at 300° F. in 5W-30 engine fill oil(CITGO grade). The data is summarized below.

    ______________________________________                                                            Two Weeks                                                                     at 300° F. in                                                          5W-30 CITGO                                                             Initial                                                                             Oil                                                       ______________________________________                                        Shore A, hardness                                                                             28      16                                                    Tensile, psi                                                                  at 50% extension                                                                              41      --                                                    at 75% extention                                                                              51      --                                                    at 100% extension                                                                             65      --                                                    at ultimate     196     137                                                   Elongation, %   520     470                                                   Volume swell, % --      27                                                    ______________________________________                                    

Adhesion test speciments were also prepared using aluminum and steelpanels which had previously been contaminated with thin films fo 5W-30engine oil. These were then allowed to cure for two weeks at roomtemperature. It was noted that cohesive failure (failure within therubber) was obtained in each case. In compounds where the adhesionpromoter was left out, adhesive failure (failure from the metalsubstrate) was noted. Adhesion on oil contaminated surfaces is anobvious advantage in maintaining an oil leak-free seal on automotiveengine flanges.

It should be noted that the adhesion promoter was not pre-equilibratedwith the oxime crosslinker in the above example.

EXAMPLE 5

Example 4 was repeated except that the polydimethylsiloxane treatedfumed silica level was increased from 3.58 to 5.09 weight percent. Thefollowing performance properties were measured.

    ______________________________________                                                            Two Weeks                                                                     at 300° F. in                                                          5W-30 CITGO                                                             Initial                                                                             Oil                                                       ______________________________________                                        Shore A, hardness                                                                             31      22                                                    Tensile, psi.                                                                 at 50% extension                                                                              51      --                                                    at 75% extention                                                                              65      --                                                    at 100% extension                                                                             79      --                                                    at ultimate     211     168                                                   Elongation, %   490     530                                                   Volume swell, % --      27                                                    ______________________________________                                    

Again, the same excellent adhesion results were obtained.

While in accordance with the patent statutes, the best mode andpreferred embodiment have been described in detail, the scope of theinvention is not be limited thereto, but rather limited by the scope ofthe attached claims:

What is claimed is:
 1. A room temperature vulcanizable silicone rubbercomposition comprising:from about 25 to 90 percent by weight based uponthe total weight of the composition of a devolatilized silanolterminated diorgano-siloxane base polymer having a viscosity from about2,000 to about 250,000 centipoises at 25° C. wherein said organo groupsare the same or different and are selected from the group consisting ofan alkyl having from 1 to 8 carbon atoms, a cycloalkyl having from 4 to7 carbon atoms, an alkenyl having from 2 to 8 carbon atoms, an aryl oran alkyl substituted aryl having from 6 to 14 carbon atoms, and afluoroalkyl having from 1 to 8 carbon atoms; from about 0 to about 40percent by weight based upon the total weight of said composition of adevolatilized diorganopolysiloxane fluid plasticizer terminated withtriorganosiloxy groups, said organo groups selected from the groupconsisting of alkyl having 1 to 8 carbon atoms, cycloalkyl having 4 to 7carbon atoms, alkenyl having 2 to 8 carbon atoms, aryl or alkylsubstituted aryl having 6 to 14 carbon atoms and fluoroalkyl having 1 to8 carbon atoms said plasticizer having a viscosity from about 50 toabout 100,000 centipoises at 25° C.; and 0.5 to 3 percent by weight ofan adhesion promoter of the formula: ##STR7## wherein R¹ and R⁶ areindependently non-aromatic hydrocarbyl or halohydrocarbyl groups orcarboxyalkyl groups having 1 to 10 carbon atoms; R², R³, R⁷ and R⁸ areindependently H, hydrocarbyl, halohydrocarbyl or carboxyalkyl having 1to 10 carbon atoms; R⁴ and R⁵ are divalent hydrocarbyl orhalohydrocarbyl groups of 1 to 10 carbon atoms; a and e are 0 to 2; band f are 1 to 3; q and h are 0 or 1 and a+b+g=f+e+h=3.
 2. A compositionas in claim 1 where g and h are
 0. 3. A composition as in claim 2 whereR¹ and R⁶ are methyl or ethyl.
 4. A composition as in claim 1 where R⁴and R⁵ are --(CH₂)₃ --.
 5. The composition of claim 1 further comprisingan effective amount of a thixotropic agent to impart non-sag propertiesto the composition.
 6. A composition as in claim 1 further comprising anoxime crosslinking agent and an organotin catalyst.
 7. A composition asin claim 6 wherein the said catalyst is present in an amount in therange of 0.01-0.5 percent based on total composition weight.
 8. Acomposition as in claim 6 wherein the catalyst is selected fromdibutyltin dilaurate; dibutyltin diacetate; tin octoate;dimethyltindibutyrate; triethyl tin tartrate; tin oleate; dibutyltinoxide and dimethyltinbis neodecanoate.
 9. A composition as in claim 1further comprising between 1% and 60% by weight of a filler.